Technical Field
The present disclosure relates to a power converter.
Description of Related Art
Power converters, such as variable-frequency drives for driving electric machines, SVGs (Static Var Generator) in the power quality management field, and APFs (Active Power Filter), play an increasingly important role in the aspects of saving power and improving power quality. In many industrial fields, the power converters are more widely promoted and applied, and produce good economic and social benefits.
A MVD (Medium Voltage Drive) is a typical representative of power converters. A feature of a conventional power converter is that the power grid side connector terminal of the power converter requires a bulky and expensive phase-shifting transformer. Secondary side of the phase-shifting transformer is connected with diode rectifier circuits of many low-voltage single-phase power modules. The low-voltage single-phase power modules are connected in series to output a desired medium voltage. Each of the low-voltage single-phase power modules has a DC bus capacitor module. Therefore, the biggest drawback of the MVD is the requirement of the bulky and expensive phase-shifting transformer. In addition, power converter circuit part of the MVD requires a large number of DC bus capacitor modules, so the overall volume is huge and the costs are high.
In order to solve the foregoing problem, another kind of MVD based on power devices (e.g., IGBT/Diode) tandem technology has been proposed. One of advantages of the MVD is that the MVD no longer requires the bulky and expensive phase-shifting transformer. However, there exist different degrees of distribution among the DC bus capacitor modules of the MVD. For example, each phase of converter circuits is equipped with the corresponding DC bus capacitor module(s), and a bus bar is connected to a common connection point of the DC bus capacitor modules. The problem that arises is the product is equipped with a relatively large number of capacitors and the cost is increased, and the capacitors occupy a large space and thereby result in lower power density. In addition, there also exist risks of internal shocks among the distributed DC bus capacitor modules.
Accordingly, how to decrease volume of a power converter, increase power density, save manufacturing costs and transportation costs, and save space required for product installation become an important issue to be solved by those in the industry.